1. Field of the Invention
This invention relates to a reinforcing apparatus for a lever handle of a door lock, more particularly to a reinforcing apparatus which can return and maintain the lever handle at its original unoperated position after the lever handle is operated to lock or unlock the door lock.
2. Description of the Related Art
The improvement of this invention is directed to a conventional door lock, as shown in FIG. 2, which includes a latch housing (A), a driving mechanism that consists of a retractable bolt-operating unit (B) and a pair of driving shafts (C), a pair of mounting caps (D), a knob (E), and a lever handle (F).
Referring to FIGS. 1 and 2, the latch housing (A) is mounted on a door (not shown) and has a pair of outer sleeves (A') extending axially outward from two opposite sides of the latch housing (A). The retractable bolt-operating unit (B) is mounted within the latch housing (A) for actuating a bolt (not shown) of the door lock in order to lock or unlock the door lock. The driving shafts (C) extend axially outward from the bolt-operating unit (B) through the outer sleeves (A') of the latch housing (A) respectively, and engage the retractable bolt-operating unit (B) by means of two driving flanks (C') so as to operate the bolt-operating unit (B) when the driving shafts (C) are rotated. The outer sleeves (A') have outwardly threaded portions located at exteriors of two opposite outer side walls of the door. The mounting caps (D) are mounted threadably and respectively on the outwardly threaded portions of the outer sleeves (A') and are connected threadably to the opposite outer side walls of the door, thereby fixing the door lock on the door. The knob (E) is connected to the right one of the driving shafts (C) for operating the bolt-operating unit (B) via the right driving flank (C') when the knob (E) is rotated. A compression spring (G) is disposed within the latch housing (A) for biasing the bolt-operating unit (B) to its original unoperated position where the right driving shaft (C) and the knob (E) are returned to their original unoperated positions. The lever handle (F) is connected to the left one of the driving shafts (C) and has the same function as that of the knob (E).
Because the center of gravity of the knob (E) is located at the axis of the right driving shaft (C), there is no torque formed between the axis of the right driving shaft (C) and the center of gravity of the knob (E). Accordingly, the compression spring (G) does not suffer from elastic fatigue even if the knob (E) has been used for a long period.
However, since the center of gravity of the lever handle (F) is located apart from the axis of the left driving shaft (C), a torque is formed between the axis of the left driving shaft (C) and the center of gravity of the lever handle (F). Thus, the compression spring (G) suffers easily from elastic fatigue after the lever handle (F) has been operated for many times. As a result, it is difficult to maintain the lever handle (F) at its original unoperated position only by means of the compression spring (G). Moreover, the left driving shaft (C) is liable to damage due to the application of excess operating forces on the lever handle (F). Thus, the door lock may easily break down.
The basic U.S. patent application No. 08/312,705 discloses a reinforcing apparatus for a lever handle of a door lock. The door lock has a driving mechanism which is to be mounted on a door for actuating a bolt of the door lock in order to lock or unlock the door lock. The driving mechanism has a driving shaft which extends axially and outwardly therefrom. The lever handle is connected to the driving shaft for operating the driving mechanism so as to actuate the bolt.
The reinforcing apparatus includes a housing which is provided around the driving shaft and which is fixed to the door, a rotary member which is received in the housing and which is mounted to the driving shaft for rotating simultaneously with the driving shaft, and means for biasing the rotary member to return and maintain the lever handle at its original unoperated position after the rotary member is rotated by the lever handle. The biasing means is mounted to the housing. The housing has a housing part with a wall transverse to the driving shaft, and a covering part opposite to the wall of the housing part. The wall of the housing part has a hole formed therethrough for passage of the driving shaft and a recessed area formed around the hole to receive the rotary member. The covering part is connected to the housing part so as to enclose the rotary member within the housing part. The rotary member has an annular plate sleeved on the driving shaft. The annular plate has an engagement tongue which projects radially and inwardly from an inner circumferential edge thereof to engage the driving shaft, and a pair of positioning lugs which project axially from an outer circumferential edge thereof and which are spaced diametrically from each other. The biasing means includes a flat spiral spring which is mounted on the annular plate and which has two legs that extend radially outward to abut respectively against the positioning lugs of the annular plate. The housing further includes a pair of diametrically opposite stopping protrusions formed on the wall of the housing part. Each of the stopping protrusions is aligned radially with and is located outwardly of a respective one of the positioning lugs of the annular plate. The stopping protrusions are engageable with the legs of the flat spiral spring.